Floating tape head having side wings for longitudinal and azimuth play back with minimized tape wrap angle

ABSTRACT

A tape recording and playback unit records and reads back data from tape either in a high track density standard format or alternatively reads back data from a tape previously recorded on another unit in accordance with a previous low density standard track format. The unit includes a primary head positioning mechanism for positioning a primary multi-channel write/read head and a secondary head positioning mechanism for positioning a secondary read-only head. The secondary head may be positioned angularly to read longitudinal and azimuth track patterns, and also to be retracted when not needed.

REFERENCE TO RELATED APPLICATION

[0001] This is a continuation application of co-pending U.S. patentapplication Ser. No. 09/149,769, filed on Sep. 8, 1998, and entitled:“FLOATING TAPE HEAD HAVING SIDE WINGS FOR LONGITUDINAL AND AZIMUTH PLAYBACK WITH MINIMIZED TAPE WRAP ANGLE”. The contents of U.S. patentapplication Ser. No. 09/149,769 are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to tape drives, and moreparticularly the present invention relates to a linear digital tapedrive having a backward-compatible auxiliary head and head positioningassembly enabling read back of outdated standard tape formats.

BACKGROUND OF THE INVENTION

[0003] Magnetic tape is widely used for recording digital information.One extensive use of digital tape recording is to provide backup andarchival storage of vast quantities of digital information, such asrecords comprising blocks of data. In some applications archival recordsare recorded on tape in a particular tape format which follows agreedstandards at the time the recording was made. The tape may then beplaced into archival storage and not retrieved until months or yearshave passed by. It is not uncommon to specify the useful storage life ofrecorded digital tapes and cartridges at thirty years, or longer.Whatever may be the useful life of a particular magnetic tapes, aprimary assumption on the part of those who store such tapes away isthat the recorded information may be read at some date in the future, ifaccess to the archived data is required.

[0004] While a particular tape and cartridge may remain functional overmany years after being in archival storage, tape transport mechanismstypically do not last nearly so long. Standardized tape recordingformats are also susceptible to evolutionary changes and improvements.These changes are primarily driven by improvements in magnetic tape andmagnetic head technologies which enable much larger data records andfiles to be stored on a given area of magnetic tape. One recentdevelopment, first employed in the hard disk drive industry, and morerecently applied to tape recording, has been the introduction of headassemblies formed of thin film inductive, and magneto-resistive, andgiant magneto-resistive (MR) read elements. These elements are typicallyfabricated in processes including photolithographic patterning steps ofthe type first developed for use by the semiconductor industry. Onedesirable aspect of these new thin film MR heads is that head gap widthsmay be narrowed considerably. Narrower head gaps and finer grainmagnetic media coatings on tape mean that many more lineal data tracksmay be defined across a magnetic recording tape of a standard givenwidth (such as one-half inch tape). Also, the head structure may beformed as a single small composite structure on a common base orsubstrate and have as many as 12, or more, distinct heads. By using acommon substrate, the heads may be formed to be in a predeterminedprecise alignment relative to nominal track locations defined along themagnetic tape. With e.g. 12 write and read head elements of the headstructure in precise alignment with the defined nominal track locations,and with large scale integrated chips providing multiple data write/readchannels, it has now become practical to have e.g. 12 channels forsimultaneously writing user data to tape and for reading user data backfrom tape. This increase in the number of write/read channelseffectively increases the overall data transfer rate between a hostcomputer and the tape drive, and enables the tape drive to becharacterized as having higher performance than previously available.

[0005] In order to take full advantage of the new thin film MR headtechnology in tape drives, a track layout which differs from previousstandard track formats is required. This new track layout employs tracksof much narrower track width and pitch. Since the write/read heads aregrouped together on a common fabrication substrate, the data tracks arealso grouped together. In one arrangement, the data tracks are groupedinto bands, or zones, across the tape, such that e.g. ten lateral headpositions relative to the tape within a single zone would access 120tracks. When a zone boundary is reached, the head structure or assemblyis then displaced laterally relative to the tape travel path to the nextzone, and the tracks of that zone then become accessible. Because trackwidths are very narrow, enabling track densities of e.g. 2000 tracks perinch, or higher, lateral tape motion must be followed in order to keepthe new head assemblies in alignment with the tracks during tape travelpast the head. Magnetic servo patterns written onto the tape may be readby servo readers and used to generate position error signals used by aclosed loop positioner to correct head position. Alternatively, opticalservo patterns embossed or otherwise formed on a back side of the tapemay be used to provide position error signals, as disclosed for examplein commonly assigned, co-pending U.S. patent application Ser. No.09/046,723 filed on Mar. 24, 1998, and entitled: “Multi-Channel MagneticTape System Having Optical Tracking Servo”, the disclosure thereof beingincorporated herein by reference.

[0006] The later high-density track format differs from previousstandard formats. For example, FIG. 1 shows an existing standard tapeformat employing longitudinal recording. In this example a magneticrecording tape 10 has a series of parallel longitudinal tracks. Threetracks 12A, 12B and 12C are shown in the FIG. 1 example, although moretracks, such as 24, 48, 96 or 128 tracks may be employed in a one-halfinch tape lineal format in accordance with a particular standardizedtrack layout plan. A head assembly 14 includes e.g. discrete inductiveread or write head elements 14A, 14B and 14C which are aligned with thetracks 12A, 12B and 12C. Other tracks may be accessed by displacing thehead assembly 14 laterally relative to the direction of the tape along apath indicated by the vertical arrows axial aligned with the head 14 inthe FIG. 1 view.

[0007] Another preexisting standard tape format employs azimuthrecording of the data tracks, i.e. adjacent tracks are recorded withmagnetic gaps oblique to each other, creating what appears generally asa “herringbone” pattern, shown in FIG. 2. Therein, one track 16A has itsmagnetic flux reversal pattern aligned with a first azimuth angleoblique to the tape travel direction, and an adjacent track 16B has itsmagnetic flux reversal pattern aligned with a second azimuth angle in anopposite sense of the first angle relative to a travel path of themagnetic tape 10. One known advantage derived from azimuth recording isthat lineal guard bands or regions between tracks may be reduced, andthe tracks may be placed closer together and read back withoutinterference from adjacent tracks. While azimuth recording technologyincreases track density somewhat, complications arise in writing andreading the slanted tracks. Multi-element tape heads, such as the tapehead 100 shown in FIGS. 4-6 of U.S. Pat. No. 5,452,152, can be providedwith some of the write/read elements having magnetic gaps aligned withone azimuth angle, and other write/read elements having magnetic gapsaligned with the other azimuth angle. Such heads are then positionedlaterally relative to the direction of tape travel in order to come intoalignment with particular tracks. An alternative approach, also shown inFIG. 2 and enabling compatibility with both the longitudinal tracks 12A,12B and 12C of the FIG. 1 example, and the azimuth tracks 16A and 16B ofthe FIG. 2 example, calls for rotating a head 19 having perpendicularhead elements 19A and 19B between the two azimuth formats and thelongitudinal format. One example of a multi-element head is given incommonly assigned, co-pending U.S. patent application Ser. No.08/760,794 filed on Dec. 4, 1996, and entitled: “Four Channel Azimuthand Two Channel Non-Azimuth Read-After-Write Longitudinal MagneticHead”, the disclosure thereof being incorporated herein by reference. Anexample of an azimuth tape recording pattern and an apparatus forwriting the pattern in accordance with servo information read back froman adjacent track is given in commonly assigned U.S. Pat. No. 5,371,638,the disclosure thereof being incorporated by reference.

[0008]FIG. 3 illustrates a newer track format plan employing a tape 10Acarrying high recording density magnetic media. According to the FIG. 3track plan, a multiplicity of data tracks 20n are distributed acrosse.g. five zones 22A, 22B, 22C, 22D and 22E. A monolithic thin film headelement 24 within the head assembly includes e.g. 12 write-read elementsin relatively close proximity enabling writing to and reading fromtracks of a particular zone, e.g. zone 22D in the FIG. 3 example. Otherzones may be accessed by displacing the head assembly laterally relativeto the direction of travel of tape 10A. Further details of a tape andtape drive in accordance with this general approach may be found in theabove-referenced U.S. patent application Ser. No. 09/046,723.

[0009] While the standardized longitudinal recording patterns shown inthe FIG. 1 example, and the azimuth recording patterns shown in the FIG.2 example, have worked very well for a number of years, newer higherdensity track layout patterns and plans, enabled by multi-element thinfilm head as well as improvements in tape media technologies are nowproposed and will most likely become standard approaches in the futurefor certain categories of longitudinal digital tape recording methodsand devices. Since extensive cartridge handling equipment in use iscapable of handling standard cartridges containing tape having the newerformat, no compelling need has arisen to change the cartridge formfactor or major features in order to accommodate the new tape trackformats enabled by emerging new technologies. Yet, a hitherto unsolvedneed has remained for backward compatibility within tape drive unitshaving monolithic multi-element heads by enabling reading back of olderpreexisting tape formats recorded on tape carried in standard tapecartridges, but based on discrete head elements, in order to recoverarchival data recorded on the older tapes.

SUMMARY OF THE INVENTION WITH OBJECTS

[0010] A general object of the present invention is to provide abackward compatible head and head positioning assembly within a lineardigital tape drive in a manner overcoming limitations and drawbacks ofprior approaches.

[0011] Another object of the present invention is to enable a lineardigital tape drive primarily adapted to recording and reading back oftrack patterns of standard cartridge tape recorded in a higher densitytrack format to also be able to read back older lower density trackpatterns of archival standard cartridge tape in order to be able toretrieve archived user data.

[0012] Yet another object of the present invention is to provide asecondary head positioning and read-only tape head module for backwardcompatibility in reading tape recorded in a low density format andcarried in standard tape cartridges as well as to provide a primary headpositioning and write-read tape head module for forward compatibility inreading tape recorded in a high density format and carried in the sametype of standard tape cartridges.

[0013] One more object of the present invention is to provide a“button-shaped” multi-element magnetic recording head which is capableof contacting a magnetic tape at a very slight tape wrap angle, andwhich may be rotated between positions aligning a magnetic recording gapof an element of the head with both longitudinal and azimuthal recordingpatterns of a lineal data track recorded on the tape.

[0014] One more object of the present invention is to provide a tapehead having side wings and dimensions less than tape width such that thetape head floats in close proximity to a tape with minimized contact,ensuring effective operation with both longitudinal and azimuthalrecording patterns as well as minimal wear and reliable long usefullife.

[0015] Accordingly, a tape recording and playback unit is provided forrecording and playing back digital data recorded along a multiplicity ofparallel longitudinal data tracks of a magnetic storage tape. The tracksare arranged in accordance with a standardized high density track layoutin which the tracks have much smaller track widths and are much moreclosely spaced together than tracks defined by older lower densitystandard tape track formats. The unit includes a base, and has a take-upreel. In one preferred form, the unit receives a single reel cartridgeand couples to an outer end of a tape supply held on a supply reel ofthe cartridge and threads the tape along a tape path defined by pluralguide rollers within the unit until the take-up reel is reached.

[0016] In order to write to and read from tape tracks in accordance withthe standardized high density track layout, the unit is equipped with aprimary head positioning mechanism. The primary mechanism is referencedto the base and presents a multi-channel primary write/read headassembly to the tape along the tape path. A coarse servo, preferablyincluding a lead screw and nut follower provides coarse elevationalcontrol to the primary write/read head assembly. A fine position servo,preferably including a voice coil motor carried on a body of the nutfollower provides fine adjustments to head position in accordance withposition error signals. Most preferably, the position error signals areprovided via an optical sensor reading optical servo patterns formed ona back side of the high density tape.

[0017] In order to provide backward compatibility with lower densitystandard tape track layouts, a secondary head positioning mechanism isalso provided within the unit. The secondary head positioning mechanismsupports and positions a read-only secondary head assembly relative tothe tape. The secondary head positioning mechanism also preferablyincludes a coarse positioner for elevational positioning. In onepreferred form, the secondary head positioning mechanism also includes amechanism for rotating the head to enable read back of longitudinalrecording, azimuth recording, and to assume a retract position when atape recorded with a lower density standard track pattern is notpresent. Most preferably, the coarse positioner of the secondarymechanism is mechanically coupled to the coarse positioner of theprimary mechanism, in order to eliminate a second coarse positionermotor. Coupling via spur gearing between the two mechanisms is presentlypreferred. The electronics of the unit may be switched between theprimary mechanism and the secondary mechanism, based upon sensing aparticular track format standard type. In one preferred form, formatsensing is by way of a unique structural feature provided on anotherwise standard tape cartridge, such that the feature distinguishesbetween high density and low density tape track standard formats.

[0018] A secondary read-only head body has a dimension less than a widthof the tape and employs a minimized tape wrap angle. The head body hasside wings enabling the head to “float” adjacent to the tape at theminimum wrap angle and effectively operate at longitudinal as well asazimuth play back angles.

[0019] These and other objects, advantages, aspects, and features of thepresent invention will be more fully appreciated and understood uponconsideration of the following detailed description of preferredembodiments presented in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In the Drawings:

[0021]FIG. 1 is a highly diagrammatic elevational view of a segment ofmagnetic data storage tape recorded with a series of lineal tracksemploying longitudinal recording in accordance with a first preexistingindustry standard tape format.

[0022]FIG. 2 is a highly diagrammatic elevational view of a segment ofmagnetic data storage tape recorded with a series of lineal tracksemploying azimuth recording in accordance with a second preexistingindustry standard tape format.

[0023]FIG. 3 is a highly diagrammatic elevational view of a segment ofmagnetic data storage tape recorded with a multiplicity of high densitylineal tracks in accordance with a new high-density recording format.

[0024]FIG. 4 is simplified diagrammatic plan view of a tape drive anddata tape cartridge wherein the tape drive includes abackward-compatible head and head positioning mechanism adapted to readthe first and second preexisting industry standard tape formats as wellas a high-density multi-channel head and head positioning mechanismadapted to read and write the new high-density recording format, inaccordance with principles of the present invention.

[0025]FIG. 5 is an enlarged isometric view of the backward-compatiblehead and head positioning mechanism shown in the FIG. 4 tape drive, inaccordance with principles of the present invention.

[0026]FIG. 6 is a top plan view of the FIG. 5 head and positioningmechanism.

[0027]FIG. 7 is a back side view in elevation of the FIG. 5 head andpositioning mechanism.

[0028]FIG. 8 is a side view in elevation of the FIG. 5 head andpositioning mechanism.

[0029]FIG. 9A is a front view in elevation of the FIG. 5 head andpositioning mechanism in a perpendicular orientation relative to tapetravel for playback of longitudinally recorded data tracks in accordancewith the FIG. 1 format.

[0030]FIG. 9B is a front view in elevation of the FIG. 5 head andpositioning mechanism in a first azimuth orientation relative to tapetravel in e.g. a forward direction for playback of one set ofazimuthally recorded data tracks in accordance with the FIG. 2 format.

[0031]FIG. 9C is a front view in elevation of the FIG. 5 head andpositioning mechanism in a second azimuth orientation relative to tapetravel in a reverse direction for playback of a second set ofazimuthally recorded data tracks in accordance with the FIG. 2 format.

[0032]FIG. 9D is a front view in elevation of the FIG. 5 head andpositioning mechanism in a third azimuthal orientation assumed by thehead at a head retract position.

[0033]FIG. 10 is an enlarged diagrammatic plan view of the retractmechanism of the FIG. 5 head and positioning mechanism.

[0034]FIG. 11 is a diagrammatic view in elevation of the spur-gearcoupling arrangement between the lead screws of the main headpositioning mechanism and the backward-compatible positioning mechanismof the FIG. 4 tape drive.

[0035]FIG. 12 is a simplified electrical block diagram of the FIG. 4tape drive.

[0036]FIG. 13 is an enlarged isometric view of the backward-compatiblehead of the FIG. 4 tape drive.

[0037]FIG. 14 is an enlarged front view in elevation of the FIG. 13head.

[0038]FIG. 15 is an enlarged side view in elevation of the FIG. 13 head.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0039] Referring to the drawings, where like reference numeralsdesignate like or corresponding parts throughout the views, FIG. 4presents a tape unit 100 and single-reel tape cartridge 102. Thecartridge 102 includes a supply reel 104 and a pancake 106 of spooledmagnetic recording tape 10A, capable of being written at a high trackdensity. Tape cartridge 102, while occupying the same physical envelopeor form factor as prior standards cartridges, has at least one uniquestructural feature, such as a uniquely located “beginning of tape” (BOT)hole in accordance e.g. with commonly assigned U.S. Pat. No. 5,790,337to Steinberg et al., and entitled: “Tape Cartridge Qualified byLocation, and Identified by Geometry, of Type Aperture”, the disclosurethereof being incorporated herein by reference. Alternatively, thecartridge 102 may be provided with a structural feature comprising auniquely located notch 107, for identifying the tape 10A as high densityrecording tape. A tape-type sensor 109 associated with a cartridgereceiver portion of the tape unit 100 may be provided to sense the notch107 and thereby to inform electronics of the unit of the particular tapetype. Other physical features, such as an embossed optical servo patternformed on a back side of the tape may also provide a unique structuralfeature for indicating a high track density tape. When a unique BOThole, or the notch 107, is not sensed at a particular cartridge, theunit 100 is alerted that the tape format (if any) of the particularcartridge is in accordance with a prior standards track format, andcalls for use of an auxiliary read-only capability present within theunit 100. An outer end of the tape pancake 106 is buckled by a suitablebuckling mechanism to a leader extending from a take-up reel 108 of thetape unit 100. A presently preferred form of tape buckling mechanism isdescribe in commonly assigned, co-pending U.S. Pat. No. 5,971,310, filedon the same date as this application and entitled: “Positive EngagementBuckle for a Tape Drive and Cartridge”, the disclosure thereof beingincorporated herein by reference. An alternative form of bucklingmechanism is described in commonly assigned U.S. Pat. No. 5,769,346 toDaly, and entitled: “Tape Buckling Mechanism for Single Reel CartridgeTape Recording”, the disclosure thereof being incorporated herein byreference. A tape supply reel motor 242 and a take-up reel motor 244 areprovided in the tape unit 100 (see FIG. 12) but are not shown in theFIG. 4 diagrammatic plan view.

[0040] Four tape guide rollers 110, 112, 114 and 116 guide the tape 10Afrom the supply reel 106 to the take-up reel 108. Two of the rollers 110and 112 are formed on a frame 118, and two of the rollers are mounted toa frame 120. The frames 118 and 120 are secured to a base 122 of theunit 110. A primary head positioning mechanism 124 is secured to thebase 122 at a location between guide rollers 112 and 114. The primarypositioning mechanism 124 includes a primary multi-channel write/readhead assembly 126 for writing and reading user data onto and from thetape 10A in accordance with a standardized higher density track layout,e.g. of the FIG. 3 type. The mechanism 124 also includes a frame 128supporting a rotating primary lead screw 130. A stepper motor 132, shownin FIG. 11, rotates the primary lead screw 130. A primary head block 134displaces the primary head 126 laterally across the tape 10A as theprimary lead screw 130 is rotated by the stepper motor 132.

[0041] In this particular tape unit 100, the high density tape 10Aincludes longitudinal servo patterns or tracks formed on the back sidethereof e.g. during manufacturing. An optical servo head 134 alsomounted to the primary head block 134 adjacently faces a back side ofthe tape 10A and optically senses the longitudinal servo patterns inorder to generate position error signals which are fed into a fineposition servo loop (FIG. 12) and result in voice coil driving currentsapplied to operate a primary voice coil motor 136, also a part of theprimary head block 134. During data writing and reading operations, thefine position servo loop keeps the primary head 126 in alignment withthe data track locations in the presence of disturbances, such aslateral tape motions and vibrations imparted to the tape 10A along thetape path. As already noted, the optical servo patterns formed on theback side of a high density tape 10A may be sensed to determine that aparticular cartridge contains high density format tape.

[0042] Also present in the FIG. 4 plan view is a secondary headpositioning mechanism 140. As may be seen in greater structural detailin FIGS. 5-9, the secondary mechanism 140 includes a frame 142 which maybe secured to the base 122 of the tape unit 100. Preferably, themechanism 140 is formed as a unitary module which may be attached to andremoved from the base 122 as a single unit. Suitable electrical plugsand cables enable the mechanism 140 to make necessary electricalconnections with the tape unit 100. The mechanism 140 selectivelypositions a secondary read-only head assembly 144 adjacent to the tape10A along the tape path at a location between the guide rollers 114 and116. The secondary mechanism 140 also includes a secondary lead screw146 rotatably mounted to the frame 142 and a secondary head block 148having a follower-nut portion engaging the secondary lead screw 146 suchthat as the screw 146 rotates, the head block 148 is translatedelevationally relative to the frame 142. The secondary head block 148rotatably mounts a lateral head shaft 150 which has one end thereofsecured to the secondary head assembly 144. A guide post 152 extendingfrom the frame 142 is followed by a guide post follower portion 154 ofthe secondary block 148 to prevent the block from rotating relative tothe frame 142 as the secondary lead screw 146 is rotated.

[0043] The lateral head shaft 150 is rotated by e.g. a rotary voice coilmotor 156 comprising a voice coil 158 attached to the shaft 150 and astator magnet assembly 160 attached to the secondary block 148. Drivingcurrent applied to the voice coil 158 causes the shaft 150 to rotatebetween e.g. four positions: retract, azimuth forward, longitudinal, andazimuth reverse. An optical encoder 162 provides an optical feedbacksignal marking the angular location of each shaft position. The encoder162 comprises a rotating reticle plate 164 mounted to the head shaft 150and a photo detector unit 166 mounted to the stator magnet assembly 160.As shown in FIG. 10 a retract mechanism includes a pin 170 extendingradially from the shaft and a pin guide 172 mounted to the secondaryblock 148 adjacent the secondary head 144. The generally annular pinguide 172 includes an angled and stepped-in region 174. The stepped-inregion 174 is located such that when the shaft 150 is at the retractangle, the angled portion of the stepped-in region 174 forces the shaft150 to move axially away from the tape path and thereby retracts thesecondary head 144 from contact proximity with the tape. The stepped-inregion 174 may optionally include a detent feature for positivelymaintaining the shaft 150 at the retract position in the absence of anyrelease rotational force applied by the voice coil motor 156. A biasspring (not shown) preferably applies an axial bias force to the shaft150 to urge it axially toward the tape confronting position and awayfrom the stepped-in retract position.

[0044]FIGS. 9A, 9B, 9C and 9D show the four nominal angular positionscapable of being assumed by the secondary head 144. A normal orperpendicular to tape travel direction position L is shown in FIG. 9Afor use in reading longitudinally written data tracks as per the FIG. 1format, for example. An azimuth forward angle position is shown in FIG.9B, and an azimuth reverse angle position is shown in FIG. 9C. Thesepositions are used for reading azimuth track patterns shown by way ofexample in FIG. 2. The forward angle position is assumed in readingazimuth record tracks while the tape moves in a forward direction fromsupply reel 104 to take-up reel 108, while the reverse angle position isassumed in reading azimuth record tracks while the tape moves in areverse direction from take-up reel 108 back onto supply reel 104. Astepped-in retract position R is shown in FIG. 9D and represents theangular position of the head 144 while retracted from operativeproximity to the tape 10A, as shown in the FIG. 4 plan view, forexample.

[0045] The secondary read-only head assembly 144 most preferablycomprises four read elements 310, 312, 314 and 316 (shown in FIGS. 13and 14). A preamplifier IC including a preamplifier for each of the readelements is included on a flex circuit forming a part of the modularsecondary head positioning mechanism 140. Suitable electrical connectors(not shown) are provided to connect the circuitry of the secondary headpositioning mechanism to circuit board electronics of the tape unit 100.

[0046]FIG. 11 illustrates one preferred form of mechanical couplingbetween the primary lead screw 130 and the secondary lead screw 146. Inthis example, a spur gearing arrangement includes a driver gear 180attached to the primary lead screw 130. An idler gear 182 engages thedriver gear 180 and transfers rotational force to a follower gear 184secured to the secondary lead screw 146. The idler gear 182 rotatesabout a shaft 186 mounted to the base 122 of tape unit 100 at a locatione.g. equidistant from axes of rotation of the primary lead screw 130 andthe secondary lead screw 146 thereby transferring rotational forceimparted by stepper motor 132 to both lead screws 130 and 146.

[0047]FIG. 12 sets forth a simplified block diagram of the electronicsof the tape unit 100. In pertinent part, the unit 100 includes a userdata handling section and a mechanisms section. In FIG. 12, the userdata handling functional blocks are drawn the left side of adiagrammatic tape path, while the servo mechanisms functional blocks aredrawn on the right side of the tape path. The user data handling blocksinclude a user interface 202 which interfaces the unit 100 to a hostcomputing environment via a standard bus signaling convention, such as alow voltage differential SCSI bus 204. The interface block 202 connectsto an internal user and control data bus 206. Also attached to theinternal bus are a programmed data controller 208 and a block buffermemory 210. The data controller 208 regulates and controls blockformatting and performs error correction coding and decoding upon blockswritten to and read back from the tape 10 (or 10A). Blocks are assembledand deconstructed in the buffer memory 210 under direct control of thedata controller 208. Four-channel data write/read ICs 212, 214 and 216support the multi-channel primary head assembly 126 and one of the ICs212 selectively supports read-only elements of the secondary read headassembly 144. A switch 220 switches read paths of the IC 212 from theprimary head 126 to the secondary head 144 whenever a lower densitystandard format tape is sensed within the unit 100.

[0048] The unit 100 also includes a programmed servo controller 230. Theservo controller 230 has a bus 232 enabling the data controller 208 topass commands to the servo controller 230, and enabling the servocontroller to pass status information back to the data controller 208.In some embodiments where servo information embedded in magnetic datatracks is present, a connection may also exist between the servocontroller 230 and the channels 212, 214 and 216 via the data/controlbus 206.

[0049] The servo controller 230 supervises a coarse position loop 234which controls coarse head position established by the stepper motor 134of the primary head positioner mechanism 124 in accordance with trackselection values received from the data controller 208. As alreadymentioned, the stepper motor 132 simultaneously actuates lead screws 130and 146 of the primary and secondary head positioner mechanisms. Sincethe data controller 208 will learn that a particular cartridge 102 hastape recorded in accordance with a standard track format via sensor 109,coarse position will be established either with respect to primary head126 for a high density track pattern (FIG. 3) or with respect tosecondary head 146 with respect to a particular low density pattern(FIGS. 1 or 2).

[0050] The servo controller 230 also supervises a tape reel motors servoloop 240 which controls operation of a supply reel motor 242 and atake-up reel motor 244 in order to establish desired tape velocity andmaintain desired tape tension during tape travel operations of unit 100.

[0051] The servo controller 230 also supervises a servo fine positionloop 250 which includes an amplifier 252 for controlling the voice coilmotor 136 of the primary head position mechanism in accordance withservo information provided by optical sensor 134 during high densitytrack format operations with tape 10A. When a low density tape 10 issensed by sensor 109, the servo fine position loop amplifier output isswitched from the primary voice coil motor 136 to the secondary voicecoil motor 156 via a switch 254, and the servo fine position loop 250then employs position information fed back from the optical sensor 166of the secondary head positioning mechanism in order to determine andcontrol the angle of shaft 150.

[0052] By providing switches 220 and 254, duplication of electronicscircuits needed to support both the primary write/read head 126 and thesecondary read-only head 144 is minimized.

[0053] Referring now to FIGS. 13, 14 and 15, the secondary tape headassembly 144 is shown in greater structural detail. The head 144includes a generally elliptically shaped body 302 having a tapeconfronting front face, a back face secured to shaft 150 and eightsides. The body 302 is formed of a suitable material such asnon-magnetic ceramic, e.g. calcium titanate. Other materials may also beused to form the body 302.

[0054] A tape-confronting face of the body 302 includes a raisedlongitudinal plateau or mesa 304 and two recessed major side surfaces orwings, a left wing 306 and a right wing 308. The wings 306 and 308, incombination with the mesa 304 enable the body to approach the tape at avery slight tape wrap angle (e.g. one degree or less) and to be rotatedbetween positions to read back longitudinally recorded information (e.g.the FIG. 1 format) and azimuthally recorded information (e.g. the FIG. 2format) without distorting or warping the tape. Four discrete magneticread-only elements 310, 312, 314 and 316 are present at elongated wearregulated regions 318 of the longitudinal mesa 304. These elements maybe formed in accordance with techniques described in commonly assignedU.S. Pat. No. 5,426,551 entitled: “Magnetic Contact Head Having aComposite Wear Surface, and commonly assigned U.S. Pat. No. 5, 475,553entitled: “Tape Head with Self-Regulating Wear Regions”, the disclosuresof these patents being incorporated herein by reference.

[0055] As shown in FIG. 14, the read-only elements 310, 312, 314 and 316are spaced apart such that desired alignment is achieved with tracksfollowing the longitudinal format (FIG. 1) as well as tracks followingthe azimuth format (FIG. 2). A plus or minus 9.1 degree rotation isemployed for azimuth read out in accordance with the FIG. 2 standardtrack pattern. Most preferably, a distance of 0.056 inch separates theread-only elements 310 and 312 and the read-only elements 314 and 316. Adistance of 0.210 inch separates element 310 from element 314, andseparates element 312 from element 316. The mesa 304 is approximately0.02 inch across and follows a radius of curvature of approximately 0.25inch. The preferred longitudinal dimension (hi) of the head body 302along the mesa 304 is 0.407 inch which is less than the nominal width(tw, e.g. 0.5 inch) of the tape 10. The body 302 has a transversedimension (tw) of 0.300 inch as measured generally along the directionof tape travel. The wings 306 and 308 are recessed below the mesa 304 bya recess dimension (mh) most preferably lying in a range between fiveand 20 microinches. A chamfer 320 is formed along the tape facing edgesof the body 302 and follows a radius of curvature of approximately 0.5inch.

[0056] When the secondary head 144 is rotated to a tape confrontationposition (FIGS. 9A, 9B or 9C) only a minimal tape wrap angle is requiredfor operation, most preferably about one degree of tape wrap, or less.This ever-so-slight wrap angle suggests that the read-only head 144floats in close proximity to the tape with minimized contact, ensuringminimal wear and reliable long useful life as well as effectiveoperation with both longitudinal and azimuthal recording patterns. Theminimized wrap angle also enables the head 144 to have a dimension lessthan the tape width without need for outriggers or other structureextending the major dimension of the head to be in excess of the tapewidth (tw) and aids realization of a truly compact secondary module 140.

[0057] Not all units 100 need be equipped with the secondary module 140.In multi-drive libraries, perhaps only one drive unit 100 need beequipped for backward compatibility by including the module 100.However, units 100 will be provided with structural and electricalfeatures and functions enabling field installation of the secondarymodule 140, should a user require addition of the backward compatibilityfunction after the unit 100 has been installed in the user environment.Also, since the secondary module 140 is truly modular, it may be removedand replaced in the field as a unit by a service technician with minimumdisruption to operation of the drive unit 100.

[0058] It is to be understood that the particular implementationsdescribed are intended as illustrations of, and not as limiting thescope of, the claims. It will of course be appreciated that in thedevelopment of any such actual implementation, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints and that these goals will vary from oneimplementation to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill having the benefit of this disclosure.

[0059] Although the present invention has been described in terms of thepresently preferred embodiment, i.e., a backward compatible head andhead positioning assembly for a one-half inch tape linear digital tapedrive system, it should be clear to those skilled in the art that thepresent invention may also be utilized in conjunction with, for example,other tape drives employing different standard tape sizes and formats.Thus, it should be understood that the instant disclosure is not to beinterpreted as limiting. Various alterations and modifications will nodoubt become apparent to those skilled in the art after having read theabove disclosure. Accordingly, it is intended that the appended claimsshould be interpreted as covering all alterations and modifications asfall within the true spirit and scope of the invention.

What is claimed is:
 1. A head assembly for a tape drive, the tape drivereceiving a tape that is moved along a tape path, the tape having a tapewidth, the head assembly comprising: a body including a tape-confrontingface having (i) a raised central mesa, (ii) a head element secured tothe central mesa, (iii) a left side wing on one side of the centralmesa, and (iv) a right side wing on another side of the central mesa,the two side wings having face surfaces recessed relative to the raisedcentral mesa; wherein the body, including the raised central mesa, theleft side wing and the right side wing, has a major axial dimensiongenerally transverse to the tape path that is less than the tape width.2. The head assembly of claim 1 wherein the body includes a plurality ofspaced apart head elements secured to the central mesa, wherein each ofthe head elements is a magnetic read-only element.
 3. The head assemblyof claim 1 wherein the body, including the raised central mesa, the leftside wing and the right side wing, has a major dimension generallyparallel to the tape path that is less than the tape width.
 4. The headassembly of claim 1 wherein the tape-confronting face is generallyellipsoidal shaped.
 5. The head assembly of claim 4 wherein the body,including the raised central mesa, the left side wing and the right sidewing, has a major dimension generally parallel to the tape path that isless than the tape width.
 6. The head assembly of claim 1 that isadapted for reading longitudinally recorded data tracks and furtheradapted to be rotated for reading azimuthally recorded data tracks. 7.The head assembly of claim 1 wherein the body includes a perimeter thatis chamfered.
 8. The head assembly of claim 1 wherein the major axialdimension generally transverse to the tape path is approximately eightypercent of the tape width.
 9. A head assembly for a tape drive, the tapedrive receiving a tape that is moved along a tape path, the tape havinga tape width, the head assembly comprising: a body including atape-confronting face having (i) a raised central mesa, (ii) a pluralityof spaced apart head elements secured to the central mesa, the headelements being adapted for reading longitudinally recorded data tracksand further adapted to be rotated for reading azimuthally recorded datatracks, (iii) a left side wing on one side of the central mesa, and (iv)a right side wing on another side of the central mesa, the two sidewings having face surfaces recessed relative to the raised central mesa;wherein the body, including the raised central mesa, the left side wingand the right side wing, has a major axial dimension generallytransverse to the tape path that is less than the tape width; whereinthe body, including the raised central mesa, the left side wing and theright side wing, has a major dimension generally parallel to the tapepath that is less than the tape width.
 10. The head assembly of claim 9wherein the tape-confronting face is generally ellipsoidal shaped. 11.The head assembly of claim 9 wherein the major axial dimension generallytransverse to the tape path is approximately eighty percent of the tapewidth.
 12. A tape drive including a head assembly positioned immediatelybetween a pair of guide rollers, the tape drive receiving a tape that ismoved along a tape path, the tape having a tape width, the head assemblycomprising: a body including a tape-confronting face having (i) a raisedcentral mesa, (ii) a plurality of spaced apart head elements secured tothe central mesa, the head elements being adapted for readinglongitudinally recorded data tracks and further adapted to be rotatedfor reading azimuthally recorded data tracks, (iii) a left side wing onone side of the central mesa, (iv) a right side wing on another side ofthe central mesa, the two side wings having face surfaces recessedrelative to the raised central mesa; and (v) a retract mechanism thatmoves the body between a first position in which the body contacts themagnetic tape in the tape path and a second position in which the bodydoes not contact the magnetic tape in the tape path, the retractmechanism also rotating the body to read the longitudinally recordeddata tracks and the azimuthally recorded data tracks.
 13. The tape driveof claim 12 wherein the body, including the raised central mesa, theleft side wing and the right side wing, has a major axial dimensiongenerally transverse to the tape path that is less than the tape width;wherein the body, including the raised central mesa, the left side wingand the right side wing, has a major dimension generally parallel to thetape path that is less than the tape width.
 14. The head assembly ofclaim 12 wherein the tape-confronting face is generally ellipsoidalshaped and wherein the major axial dimension generally transverse to thetape path is approximately eighty percent of the tape width.
 15. A headassembly for a tape drive, the tape drive receiving a tape that is movedalong a tape path, the tape having a tape width, the head assemblycomprising: a body adapted to read longitudinally recorded data tracksand further adapted to be rotated for reading azimuthally recorded datatracks; and a retract mechanism that moves the body between a firstposition in which the body contacts the tape in the tape path and asecond position in which the body does not contact the tape in the tapepath, the retract mechanism also rotating the body to read thelongitudinally recorded data tracks and the azimuthally recorded datatracks.
 16. The head assembly of claim 15 wherein the body includes atape-confronting face having (i) a raised central mesa, (ii) a headelement secured to the central mesa, (iii) a left side wing on one sideof the central mesa, and (iv) a right side wing on another side of thecentral mesa, the two side wings having face surfaces recessed relativeto the raised central mesa, the body having a major axial dimensiongenerally transverse to the tape path that is less than the tape width.17. (New) A tape drive that receives a tape that is moved along a tapepath, the tape having a tape width, the tape drive comprising: a pair ofguide rollers; and a head assembly that is positioned immediatelybetween the pair of guide rollers, the head assembly having a body, thebody including a tape-confronting face having (i) a raised central mesa,(ii) a head element secured to the central mesa, (iii) a left side wingon one side of the central mesa, and (iv) a right side wing on anotherside of the central mesa, the two side wings having face surfacesrecessed relative to the raised central mesa.
 18. The tape drive ofclaim 17 wherein the body, including the raised central mesa, the leftside wing and the right side wing, has a major axial dimension generallytransverse to the tape path that is less than the tape width.
 19. Thetape drive of claim 17 wherein the head assembly does not includeoutriggers that extend along the entire tape width adjacent the body.20. A head assembly for a tape drive, the tape drive receiving a tapethat is moved along a tape path, the tape having a tape width, the headassembly comprising: a body including a tape-confronting face having (i)a raised central mesa, (ii) a plurality of spaced apart head elementssecured to the central mesa, the head elements being adapted for readinglongitudinally recorded data tracks and further adapted to be rotatedfor side of the central mesa, and (iv) a right side wing on another sideof the central mesa, the two side wings having face surfaces recessedrelative to the raised central mesa; and a retract mechanism that movesthe body between a first position in which the body contacts themagnetic tape in the tape path and a second position in which the bodydoes not contact the magnetic tape in the tape path, the retractmechanism also rotating the body to read the longitudinally recordeddata tracks and the azimuthally recorded data tracks.
 21. The headassembly of claim 20 wherein the body, including the raised centralmesa, the left side wing and the right side wing, has a major axialdimension generally transverse to the tape path that is less than thetape width.
 22. The head assembly of claim 21 wherein the body,including the raised central mesa, the left side wing and the right sidewing, has a major dimension generally parallel to the tape path that isless than the tape width.
 23. A tape drive that receives a tape thatmoves along a tape path, the tape having a tape width, the tape drivecomprising: a pair of guide rollers; and a head assembly positionedimmediately between the guide rollers, the head assembly including abody, the body including a tape-confronting face having (i) a raisedcentral mesa, (ii) a plurality of spaced apart head elements secured tothe central mesa, (iii) a left side wing on one side of the centralmesa, and (iv) a right side wing on another side of the central mesa,the two side wings having face surfaces recessed relative to the raisedcentral mesa; wherein the body, including the raised central mesa, theleft side wing and the right side wing, has a major dimension generallyparallel to the tape path that is less than the tape width.
 24. The tapedrive of claim 23 wherein the body, including the raised central mesa,the left side wing and the right side wing, has a major axial dimensiongenerally transverse to the tape path that is less than the tape width.